Index: sbin/ifconfig/ifgroup.c
===================================================================
--- sbin/ifconfig/ifgroup.c
+++ sbin/ifconfig/ifgroup.c
@@ -52,12 +52,9 @@
 	memset(&ifgr, 0, sizeof(ifgr));
 	strlcpy(ifgr.ifgr_name, name, IFNAMSIZ);
 
-	if (group_name[0] && isdigit(group_name[strlen(group_name) - 1]))
-		errx(1, "setifgroup: group names may not end in a digit");
-
 	if (strlcpy(ifgr.ifgr_group, group_name, IFNAMSIZ) >= IFNAMSIZ)
 		errx(1, "setifgroup: group name too long");
-	if (ioctl(s, SIOCAIFGROUP, (caddr_t)&ifgr) == -1 && errno != EEXIST)
+	if (ioctl(s, SIOCAIFGROUP, (caddr_t)&ifgr) == -1)
 		err(1," SIOCAIFGROUP");
 }
 
@@ -70,9 +67,6 @@
 	memset(&ifgr, 0, sizeof(ifgr));
 	strlcpy(ifgr.ifgr_name, name, IFNAMSIZ);
 
-	if (group_name[0] && isdigit(group_name[strlen(group_name) - 1]))
-		errx(1, "unsetifgroup: group names may not end in a digit");
-
 	if (strlcpy(ifgr.ifgr_group, group_name, IFNAMSIZ) >= IFNAMSIZ)
 		errx(1, "unsetifgroup: group name too long");
 	if (ioctl(s, SIOCDIFGROUP, (caddr_t)&ifgr) == -1 && errno != ENOENT)
Index: sys/net/if.c
===================================================================
--- sys/net/if.c
+++ sys/net/if.c
@@ -1215,6 +1215,7 @@
 	/* Report the new if_xname back to the userland. */
 	sprintf(ifname, "%s", ifp->if_xname);
 
+	IFNET_WUNLOCK();
 	prison_free(pr);
 	return (0);
 }
@@ -1274,6 +1275,25 @@
 }
 #endif /* VIMAGE */
 
+int
+if_checkname(const char *name)
+{
+	struct ifnet		*ifp;
+	struct ifg_group	*ifg;
+
+	IFNET_LOCK_ASSERT();
+
+	TAILQ_FOREACH(ifg, &V_ifg_head, ifg_next)
+		if (!strncmp(name, ifg->ifg_group, IFNAMSIZ))
+			return (EEXIST);
+
+	TAILQ_FOREACH(ifp, &V_ifnet, if_link)
+		if (!strncmp(name, ifp->if_xname, IFNAMSIZ))
+			return (EEXIST);
+
+	return (0);
+}
+
 /*
  * Add a group to an interface
  */
@@ -1283,15 +1303,13 @@
 	struct ifg_list		*ifgl;
 	struct ifg_group	*ifg = NULL;
 	struct ifg_member	*ifgm;
+	struct ifnet		*ifp_it;
 	int 			 new = 0;
 
-	if (groupname[0] && groupname[strlen(groupname) - 1] >= '0' &&
-	    groupname[strlen(groupname) - 1] <= '9')
-		return (EINVAL);
-
 	IFNET_WLOCK();
-	TAILQ_FOREACH(ifgl, &ifp->if_groups, ifgl_next)
-		if (!strcmp(ifgl->ifgl_group->ifg_group, groupname)) {
+
+	TAILQ_FOREACH(ifp_it, &V_ifnet, if_link)
+		if (!strncmp(groupname, ifp_it->if_xname, IFNAMSIZ)) {
 			IFNET_WUNLOCK();
 			return (EEXIST);
 		}
@@ -2522,6 +2540,7 @@
 		while (namelen != 0)
 			sdl->sdl_data[--namelen] = 0xff;
 		IF_ADDR_WUNLOCK(ifp);
+		IFNET_WUNLOCK();
 
 		EVENTHANDLER_INVOKE(ifnet_arrival_event, ifp);
 		/* Announce the return of the interface. */
@@ -3602,12 +3621,25 @@
 void
 if_initname(struct ifnet *ifp, const char *name, int unit)
 {
+	char new_name[IFNAMSIZ];
+
 	ifp->if_dname = name;
 	ifp->if_dunit = unit;
+
+	IFNET_WLOCK();
+again:
 	if (unit != IF_DUNIT_NONE)
-		snprintf(ifp->if_xname, IFNAMSIZ, "%s%d", name, unit);
+		snprintf(new_name, IFNAMSIZ, "%s%d", name, unit);
 	else
-		strlcpy(ifp->if_xname, name, IFNAMSIZ);
+		strlcpy(new_name, name, IFNAMSIZ);
+
+	if (if_checkname(new_name)) {
+		unit++;
+		goto again;
+	}
+
+	strlcpy(ifp->if_xname, new_name, IFNAMSIZ);
+	IFNET_WUNLOCK();
 }
 
 int
Index: sys/net/if_clone.c
===================================================================
--- sys/net/if_clone.c
+++ sys/net/if_clone.c
@@ -217,8 +217,12 @@
 	int err;
 	struct ifnet *ifp;
 
-	if (ifunit(name) != NULL)
+	IFNET_RLOCK();
+	if (if_checkname(name)) {
+		IFNET_RUNLOCK();
 		return (EEXIST);
+	}
+	IFNET_RUNLOCK();
 
 	if (ifc->ifc_type == SIMPLE)
 		err = ifc_simple_create(ifc, name, len, params);
@@ -621,7 +625,9 @@
 	}
 
 	snprintf(name, IFNAMSIZ, "%s%d", ifc->ifc_name, *unit);
-	if (ifunit(name) != NULL) {
+	IFNET_RLOCK();
+	if (if_checkname(name)) {
+		IFNET_RUNLOCK();
 		free_unr(ifc->ifc_unrhdr, *unit);
 		if (wildcard) {
 			(*unit)++;
@@ -629,6 +635,7 @@
 		} else
 			return (EEXIST);
 	}
+	IFNET_RUNLOCK();
 
 	IF_CLONE_ADDREF(ifc);
 
Index: sys/net/if_epair.c
===================================================================
--- sys/net/if_epair.c
+++ sys/net/if_epair.c
@@ -767,10 +767,10 @@
 	*(dp+1) = '\0';
 
 	/* Check if 'a' and 'b' interfaces already exist. */ 
-	if (ifunit(name) != NULL)
+	if (if_checkname(name))
 		return (EEXIST);
 	*dp = 'a';
-	if (ifunit(name) != NULL)
+	if (if_checkname(name))
 		return (EEXIST);
 
 	/* Allocate memory for both [ab] interfaces */
Index: sys/net/if_var.h
===================================================================
--- sys/net/if_var.h
+++ sys/net/if_var.h
@@ -489,6 +489,7 @@
  * To assert the ifnet lock, you must know not only whether it's for read or
  * write, but also whether it was acquired with sleep support or not.
  */
+#define	IFNET_LOCK_ASSERT()			sx_assert(&ifnet_sxlock, SA_LOCKED)
 #define	IFNET_RLOCK_ASSERT()		sx_assert(&ifnet_sxlock, SA_SLOCKED)
 #define	IFNET_RLOCK_NOSLEEP_ASSERT()	rw_assert(&ifnet_rwlock, RA_RLOCKED)
 #define	IFNET_WLOCK_ASSERT() do {					\
@@ -554,6 +555,7 @@
 int	ifpromisc(struct ifnet *, int);
 struct	ifnet *ifunit(const char *);
 struct	ifnet *ifunit_ref(const char *);
+int if_checkname(const char *);
 
 int	ifa_add_loopback_route(struct ifaddr *, struct sockaddr *);
 int	ifa_del_loopback_route(struct ifaddr *, struct sockaddr *);